This disclosure relates generally to connections for high-pressure risers, and to methods and apparatus for assembling the connections for high-pressure risers.
When a subsea well is controlled using a surface Blow-Out Preventer (“BOP”) instead of a subsea BOP located on the seafloor, the well control activities are mainly conducted at the sea surface. Thus, using a surface BOP typically requires a high-pressure riser for providing a pressure barrier between the subsea shutoff, usually a Mudline Closure Device (“MCD”), and the surface BOP. An example of available technology to implement a high-pressure riser is to use the type of pipes that have more commonly been used for downhole casing. Also, threaded and coupled (“T&C”) connectors may be preferred for joining the pipes of the high-pressure riser. Indeed, the standard design of T&C connectors keeps the load path as close as possible to the outer diameter of the pipes, which is beneficial with the high pressures and associated large end cap forces possibly encountered in a high-pressure riser. Although the standard design of T&C connectors that are commonly employed for joining casing pipes may work adequately in a high-pressure riser, there are some important operational and technical issues that could be addressed to improve their assembly when they are used in a high-pressure riser.
When a casing is made-up of pipes with T&C connectors, the assembly systems consist of slips and tongs. In the down position, the slips grab onto the lower pipe assembly from all angles that can be engaged. In the up position, the slips release the lower pipe assembly. The slips are not capable of supporting the lower pipe assembly on the T&C connectors due to their profile that is preferably slim for a more even load distribution on the threads. Thus, the slips need to grab on the lower pipe assembly, which has a T&C connector already installed on it and facing up. The slips consist of essentially friction surfaces, which are long enough to allow sufficient friction to support the weight of the full length of the lower pipe assembly, in some cases up to 12,000 feet, which is hanging below the slips. The tongs also include a section that is similar to the slips (sometimes called the upper slips). The upper slips grab the upper pipe to be joined to the lower pipe assembly. The upper slips are attached to a portion of the tongs that will rotate when driven by the torque provided on the tongs.
This assembly method is manually highly intensive and requires a dedicated and trained crew to be executed. Further, when the make-up and break-out torque is high, the slips that are commonly used suffer from significant limitations. Slip tooth bite creates a significant distortion on the pipes, even if non-marking dies are used. This distortion makes use of coatings difficult, makes it difficult to achieve the level of corrosion protection that may be desired, and potentially generates fatigue failure. Still further, the area where the slips grab the lower pipe assembly must be bare and cannot have any obstructions. Thus, there are large areas of the pipes making the riser that are prevented from being used for setting buoyancy or other riser attachments. Finally, slips are inherently limited in the amount of torque they can provide.
There is a need for an alternate system that provides more torque capacity, and/or can hang-off the lower pipe assembly more efficiently. The assembly of the riser can preferably be done more automatically with less manual intensive labor.